Photovoltaic fluorine-containing waste acid detection method

Abstract

This invention discloses a method for detecting photovoltaic fluorine-containing waste acid, comprising the following steps: 1) obtaining the nitrate concentration c(NO3) corresponding to the absorbance value y from the nitrate standard curve. ‑ The method involves: 1) calculating the nitrate content in the photovoltaic waste acid to be tested; 2) determining the fluorosilicate content after precipitation and separation, and simultaneously filtering the precipitate to obtain the first solution; 3) determining the sulfate content using the first solution; and 4) determining the fluoride ion content using the first solution. This method is quick and simple, separating interfering components through pretreatment and performing stepwise detection on the sample in the system. When the spectrophotometer of this invention measures nitrate, other ions in the components do not interfere with the determination of nitrate, so there is no need to separate the nitrate sample.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic fluorine-containing waste acid and electronic chemical detection technology, and in particular to a method for detecting photovoltaic fluorine-containing waste acid. Background Technology

[0002] Photovoltaic waste acid emissions are enormous, causing serious environmental pollution. The main component of photovoltaic waste acid is silicon etching solution; the system itself has a low degree of contamination and high recovery value. Photovoltaic waste acid is a mixture of multiple acids, and accurate detection of each acid component is crucial for achieving fluorine resource recovery and harmless treatment of the waste acid. Therefore, establishing reliable analytical methods to detect the component content in photovoltaic waste acid not only provides analytical tools for matching silicon etching solutions but also provides quality control assurance for the treatment and recovery processes of photovoltaic waste acid.

[0003] The composition of silicon etching solutions varies depending on the production process. Currently, detection methods for recovered silicon etching solutions are proposed based on different applicable systems. For example, CN114264769A discloses a method for detecting the component concentrations of an electronic-grade mixed acid system. This method is applicable to treating 3-5 ternary strong-weak mixed acid systems containing hydrofluoric acid. The acid to be treated is a strong-weak mixed acid system containing any two of nitric acid, acetic acid, and sulfuric acid. The mixed acid is titrated with a titrant to obtain the titration endpoint. Then, specific titrants are used to titrate fluoride ions and sulfate ions in the system, and the concentrations of each ion are calculated. However, when titrating a mixed acid system containing sulfuric acid, the fluoride ions react exothermically, causing them to volatilize and affecting the fluoride ion measurement results.

[0004] CN115839973A discloses a method for detecting the content of hydrofluoric acid, fluoride, or sulfuric acid in mixed acid systems containing hydrofluoric acid, fluoride, or fluoride. This method releases fluoride ions from the mixed acid system through hydrolysis and uses potentiometric titration to analyze other anions, reducing the instability of fluoride ion determination. However, when this method is used in mixed acid systems containing fluorosilicic acid, the fluorosilicic acid decomposes and is consumed during the hydrolysis process to release fluoride ions, interfering with the accuracy of fluoride ion determination results.

[0005] Furthermore, when existing potentiometric titration methods are used for mixed acid solutions containing nitrate ions, nitrate ions and nitrite ions remain in equilibrium in the aqueous solution. At the titration endpoint, nitrite ions and hydrogen ions are generated, causing acidification of the solution and resulting in a large error in the nitrate redox titration results. At the same time, photovoltaic fluorine-containing waste acid contains fluoride ions. Due to the tendency of the acid-base electrode surface to passivate when titrating solutions containing fluoride ions, the detection sensitivity for other acids is reduced, affecting the accuracy of the titration results for photovoltaic fluorine-containing waste acid. Summary of the Invention

[0006] As described above, existing mixed acid detection methods cannot accurately detect the fluoride ion content in waste acid containing fluoride ions and sulfate ions; nitrate titration results have large errors; and fluoride ions passivate the electrode surface, reducing detection sensitivity and affecting detection accuracy. Therefore, this invention provides a method for detecting photovoltaic fluoride-containing waste acid.

[0007] The solution of the present invention is:

[0008] A method for detecting fluorine-containing waste acid from photovoltaic systems includes the following steps:

[0009] 1) Plot a standard curve for the nitrate standard. Use disulfonic acid phenol as the colorimetric reagent to measure the absorbance value y of the photovoltaic waste acid to be tested at 420 nm. Based on the absorbance value y, obtain the nitrate concentration C corresponding to that absorbance value from the standard curve of the nitrate standard. (NO3-) The mass percentage content of nitrate in the photovoltaic waste acid to be tested is calculated using the following formula:

[0010]

[0011] Among them, W (NO3-) C represents the mass percentage content of nitrate in the photovoltaic waste acid to be treated. (NO3-) denoted as nitrate concentration (mg / L) determined from the standard curve; m represents the mass (g) of the photovoltaic waste acid to be tested.

[0012] 2) After adding saturated potassium nitrate solution to the photovoltaic waste acid to be tested, the mixture was filtered to obtain potassium fluorosilicate precipitate and a first solution. After separation of the precipitate, it was decomposed in water at 100℃. The reconstituted solution was titrated with sodium hydroxide as titrant and bromothymol blue-neutral red as indicator. The fluorosilicate (SiF6) content in the photovoltaic waste acid to be tested was calculated according to the following formula. 2- Percentage content by mass:

[0013]

[0014] Among them, W (SiF62-) V represents the mass percentage of nitrate in the photovoltaic waste acid to be treated; V represents the volume (mL) of sodium hydroxide standard titration solution consumed in the titration; c represents the accurate concentration (mol / L) of the sodium hydroxide standard titration solution; M represents the molar mass of fluorosilicic acid (1 / 4H2SiF6) in grams per mole (g / mol) (M = 36.02); m represents the mass (g) of photovoltaic waste acid detected in step 1.

[0015] 3) Plot a standard curve for the sulfate standard. Prepare a suspension by adding a barium ion-containing compound to the first solution. Measure the absorbance y of the suspension at 312 nm. Based on the absorbance y, read the mass m of sulfate ions in the first solution from the standard curve of the sulfate standard. (SO42-) The mass percentage of sulfate in photovoltaic waste acid can be calculated using the following formula:

[0016]

[0017] Among them, W (SO42-) The percentage content of nitrate by mass; m (SO42-) denoted as , where is the mass (g) of nitrate ions in the solution determined based on the standard curve; m is the mass (g) of photovoltaic waste acid weighed in step 1.

[0018] 4) Plot a fluoride ion standard curve with the logarithm of the fluoride ion standard solution concentration as x and the measured potential value as y. After adding a total ionic strength adjustment buffer to the first solution and measuring the solution potential value y, determine the fluoride ion concentration in the solution from the fluoride ion standard curve. The percentage of fluoride ions in the waste acid can be calculated using the following formula:

[0019]

[0020] Among them, W (F-) The percentage of fluoride ions in photovoltaic waste acid; C (F-) The mass concentration (mg / L) is determined based on the fluoride ion standard curve; m is the mass (g) of the photovoltaic waste acid weighed in step 1; V is the volume of the test liquid prepared when testing fluoride ions (generally 0.05L).

[0021] This method, which involves precipitation and separation to remove fluorosilicate ions from photovoltaic waste acid before detecting fluoride and sulfate ions, effectively improves the accuracy of ion detection results and reduces the interference of fluorosilicate ions on the detection results of other ions. This, in turn, significantly enhances the accuracy of ion content detection results.

[0022] As a preferred technical solution, the solvent used for the saturated potassium nitrate solution in step 2) is a mixture of water and ethanol in a volume ratio of 2:1.

[0023] As a preferred technical solution, the precipitation reaction temperature in step 2) is -20℃, and the precipitation treatment time is 20 minutes. This effectively removes fluorosilicate ions from waste acid in the form of precipitation.

[0024] As a preferred technical solution, the concentration of NaOH used in the titration in step 2) is 0.5005 mol / L.

[0025] As a preferred technical solution, the total ionic strength adjusting buffer solution is a mixed solution of glacial acetic acid, sodium chloride and cyclohexanediaminetetraacetic acid, with a pH of 5.5 to 6.0.

[0026] As a preferred technical solution, the linear range for determining fluoride ions using a fluoride ion selector is 0.0019 mg / L to 1900 mg / L. In this case, the concentrations of the fluoride ion standard solutions used to plot the fluoride ion standard curve are 5 mg / L, 10 mg / L, 20 mg / L, 40 mg / L, and 60 mg / L.

[0027] As a preferred technical solution, the sulfate standard substances used to plot the sulfate standard curve have masses of 0.2 mg, 0.4 mg, 0.6 mg, and 0.8 mg.

[0028] As a preferred technical solution, the concentrations of nitrate standards used to plot the nitrate standard curve are 2 mg / L, 4 mg / L, 6 mg / L, 8 mg / L, and 10 mg / L.

[0029] A method for detecting photovoltaic fluorine-containing waste acid using the above-mentioned technical solution includes the following steps: 1) Plotting a standard curve for nitrate standards, using disulfonic acid phenol as a colorimetric reagent, measuring the absorbance value y of the photovoltaic waste acid to be detected at 420 nm, and obtaining the nitrate concentration C corresponding to the absorbance value y from the standard curve of the nitrate standards. (NO3-) 2) After adding saturated potassium nitrate solution to the photovoltaic waste acid to be tested, filter to obtain potassium fluorosilicate precipitate and the first solution. After separation of the precipitate, decompose it in water at 100℃. Titrate the redissolved solution with sodium hydroxide titrant using bromothymol blue-neutral red as an indicator. 3) Plot the standard curve of sulfate standard. Add a barium ion-containing compound to the first solution to prepare a suspension. Measure the absorbance y of the suspension at 312nm. Read the mass m of sulfate ions in the first solution from the standard curve of sulfate standard based on the absorbance y. (SO42-) 4) Plot a fluoride ion standard curve with the logarithm of the fluoride ion standard solution concentration as x and the measured potential value as y. After adding a total ionic strength adjustment buffer to the first solution and measuring the solution potential value y, determine the fluoride ion concentration in the solution from the fluoride ion standard curve.

[0030] Advantages of this invention:

[0031] This method is quick and simple, separating interfering components through pretreatment and then performing stepwise detection on the sample in the system. When the spectrophotometer measures nitrate, other ions in the components do not interfere with the determination of nitrate, therefore, there is no need for sample separation treatment of nitrate.

[0032] This method solves the technical problems existing in the mixed acid detection method, such as the inability to accurately detect the fluoride ion content in waste acid containing fluoride and sulfate ions; large errors in nitrate titration results; and the passivation of electrode surfaces by fluoride ions, which reduces detection sensitivity and affects detection accuracy. When determining nitrate and sulfate ions, this method uses the spectral absorption method, which is faster and more convenient than the traditional titration method, and is beneficial for the rapid detection, treatment process development and quality control of photovoltaic fluoride waste acid. Attached Figure Description

[0033] Figure 1 The method flowchart provided in this application is a schematic diagram.

[0034] Figure 2 This is a schematic diagram of the linear fitting results of nitrate concentration and absorbance obtained in Example 1 of this application;

[0035] Figure 3 This is a schematic diagram of the linear fitting results of sulfate mass versus absorbance obtained in Example 1 of this application;

[0036] Figure 4 This is a schematic diagram of the calibration curve of the fluoride ion selective electrode obtained in Example 1 of this application. Detailed Implementation

[0037] This invention provides a method for detecting fluorine-containing waste acid from photovoltaic systems.

[0038] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0039] See Figure 1 The photovoltaic fluorine-containing waste acid detection method provided in this application measures the anions in the above-mentioned photovoltaic waste acid in sequence. The anion determination is performed in the order of nitrate, fluorosilicate, sulfate and fluoride. Since the determination of nitrate is not affected by other anions, it is determined by ultraviolet spectrophotometry alone. Fluorosilicate, sulfate and fluoride need to be processed before analysis.

[0040] Unless otherwise specified, all materials and instruments used in the following embodiments were obtained through commercial channels.

[0041] Example 1: Measurement of Photovoltaic Waste Acid

[0042] The photovoltaic waste acid being treated contains at least the following components: hydrofluoric acid, fluorosilicic acid, sulfuric acid, and nitric acid. Due to the complex composition of the waste acid, no other components were tested.

[0043] 1. Determine the nitrate content in the photovoltaic waste acid to be treated;

[0044] In anhydrous conditions, nitrate ions in waste acid react with added disulfonic acid phenol to form nitrodisulfonic acid phenol. In an alkaline medium, molecular rearrangement occurs, generating a yellow marker. The absorbance of the reaction system after the addition of this substance is measured and is proportional to the mass concentration of nitrate within a certain range.

[0045] Based on the above principle, a serial dilution of nitrate standard (potassium nitrate) solution was performed to prepare standard solutions with nitrate concentrations of 2 mg / L, 4 mg / L, 6 mg / L, 8 mg / L, and 10 mg / L. A solution system without added nitrate was also prepared. After adding disulfonic acid phenol to each sample, the absorbance value of each sample at 420 nm was measured. A standard curve was plotted, and the linear equation was obtained. The results are shown in [reference needed]. Figure 2 The linear equation for the nitrate standard is y = 0.1026C. (NO3-) +0.002, R 2 =0.9998.

[0046] Weigh 0.3–0.4 mg of photovoltaic waste acid sample into a polytetrafluoroethylene evaporating dish, heat and dry at 60 °C, add disulfonic acid phenol after drying, and dilute to a volume of 50 mL in a volumetric flask. Pipette a certain amount of solution into a cuvette and measure the absorbance y of the sample at 420 nm using a UV-Vis spectrophotometer. Substitute the absorbance y into the above standard equation to calculate the mass concentration C of nitrate. (NO3-) Substituting these values ​​into the following formula, the mass percentage of nitrate in the treated photovoltaic waste acid can be calculated:

[0047]

[0048] Among them, W (NO3-) C represents the mass percentage content of nitrate in the photovoltaic waste acid to be treated. (NO3-) To determine the absorbance value of the photovoltaic waste acid to be treated, the nitrate concentration (mg / L) was obtained from the nitrate standard curve; m is the mass (g) of the photovoltaic waste acid to be tested.

[0049] Following the steps described above, in this embodiment, photovoltaic waste acid of different masses from the same batch was weighed, and the same operation was repeated three times. The nitrate ion content in the waste acid was measured, and the results of the three repetitions were analyzed to verify the accuracy and repeatability of the method. The nitrate content in the obtained waste acid is shown in the table below:

[0050]

[0051] The relative deviation of the results obtained from the above operation was only 0.0031, proving that the method is highly accurate and reproducible for determining the nitrate content in photovoltaic waste acid.

[0052] 2. Determine the content of fluorosilicate, sulfate, and fluoride ions in the photovoltaic waste acid to be treated:

[0053] When determining the fluorosilicate, sulfate, and fluoride ions in photovoltaic waste acid, the three anions need to be separated and measured sequentially because they interfere with each other.

[0054] 2.1 Separation of fluorosilicic acid

[0055] The principle of fluorosilicic acid separation: In a photovoltaic waste acid system where nitrate, fluorosilicate, sulfate, and fluoride ions coexist, only fluorosilicate ions will form a precipitate with potassium ions. Therefore, when a saturated potassium nitrate solution is added to the sample to be tested, potassium fluorosilicate precipitate is formed first. The fluorosilicate ions can be separated and removed by filtering the precipitate.

[0056] The reaction formula for the precipitation of fluorosilicate is: SiF6 2- +2K + →K2SiF6↓

[0057] 2.2 Determination of fluorosilicic acid content by reconstitution titration of fluorosilicic acid precipitation:

[0058] After precipitation and separation, potassium fluorosilicate decomposes in water at 100℃ to produce hydrofluoric acid. The precipitate separated on filter paper is titrated with sodium hydroxide as the titrant and bromothymol blue-neutral red as the indicator. This allows for quantitative analysis of fluorosilicate ions in the waste acid. The reaction formula is as follows:

[0059] The decomposition reaction of potassium fluorosilicate is: K2SiF6↓ + 3H2O → 2KF + H2SiO3 + 4HF

[0060] The chemical reaction for the titration of fluorosilicic acid is: HF + NaOH = NaF + H₂O

[0061] When heated in a water bath, potassium fluorosilicate decomposes to produce hydrofluoric acid. When titrated with sodium hydroxide, the solution changes from pink to light green and remains unchanged for 15 seconds.

[0062] Based on the above principle, the photovoltaic waste acid to be treated was heated in a water bath at 100°C for 5 minutes. After the solution cooled to room temperature, it was titrated with sodium hydroxide until it changed from pink to light green and remained unchanged for 15 seconds. The titration was then stopped, and the amount of sodium hydroxide solution consumed was recorded. The mass percentage of fluorosilicate in the photovoltaic waste liquid was calculated using the following formula:

[0063]

[0064] Among them, W (SiF62-)The percentage of fluorosilicate in the photovoltaic waste liquid; V is the volume (mL) of sodium hydroxide standard titration solution consumed in the titration; c is the accurate value of the concentration of sodium hydroxide standard titration solution (mol / L); M is the molar mass of fluorosilicic acid (1 / 4H2SiF6), in grams per mole (g / mol) (M=36.02); m is the mass (g) of photovoltaic waste acid weighed in step 1.

[0065] In a specific embodiment, the precipitant for fluorosilicate ions was a saturated potassium nitrate solution with a water-to-ethanol volume ratio of 2:1. The precipitation temperature was -20°C, and the precipitation time was 20 min. After filtration, the filter paper and the precipitate were placed in a polyethylene conical flask, sealed, and heated in a water bath. While still hot, the solution was titrated with 0.5005 mol / L NaOH to analyze and determine the fluorosilicate ions in the waste acid system. The results of three repeated tests show the fluorosilicic acid content in the waste acid as shown in the table below.

[0066]

[0067] 1 Note: This sample is a mixed acid sample that has not undergone precipitation treatment. It was directly titrated and analyzed using sodium hydroxide and an indicator.

[0068] 2 Note: This sample was obtained by separating other anions using a precipitation method, and the separated precipitate was then subjected to quantitative analysis of fluorosilicic acid.

[0069] As shown in the table above, the average deviation of results obtained by direct measurement of waste acid without precipitation separation is relatively high. This is because the composition of the solution is complex, and acidity adjustment is required before titration testing, thus introducing errors. However, by separating the precipitate fluorosilicate and then measuring it, no acidity adjustment is needed, and direct titration can be performed. The relative average deviation of the results is significantly reduced, and the repeatability is better. This indicates that this method can effectively solve the measurement errors caused by excessive impurities in existing waste acid methods.

[0070] 2.3 Determination of sulfate ions in photovoltaic waste acid to be treated:

[0071] Measurement principle: SO4 2- +Ba 2+ →BaSO4↓

[0072] Under neutral conditions, sulfate ions react with barium ions to form a precipitate, which, in an ethanol dispersant, forms a barium sulfate suspension. The absorbance of the resulting solution at 312 nm is measured, and the absorbance value is directly proportional to the mass concentration of sulfate ions.

[0073] Based on the above principle, a serial dilution of the sulfate standard (potassium sulfate) solution was performed to prepare standard solutions with sulfate mass concentrations of 0.2 mg, 0.4 mg, 0.6 mg, and 0.8 mg. After processing the samples at each serial dilution as described above, the absorbance value of each sample at 312 nm was measured. A standard curve was plotted and a linear equation was obtained. The results are shown in [reference needed]. Figure 3 The linear equation for sulfate is y = 0.1980m. (SO42-) +0.0025, R 2 =0.9990.

[0074] The absorbance y of the photovoltaic waste acid sample at 312 nm was measured, and the mass m of sulfate ions in the solution was calculated by substituting it into the above equation. (SO42-) The mass percentage of sulfate in the sample can be calculated using the following formula:

[0075]

[0076] Among them, W (SO42-) The percentage content of nitrate; m (SO42-) m is the mass (g) of sulfate obtained from the sulfate standard curve based on the absorbance value of the sample; m is the mass (g) of photovoltaic waste acid weighed in step 1.

[0077] In a specific embodiment, based on the obtained standard curve, such as Figure 3 As shown in the table below, the mass percentage content of sulfate in the sample was measured according to the steps described above:

[0078]

[0079] 1,2 Note: All sample data were obtained by reacting with barium chloride to form a precipitate and then substituting the results into the standard equation. 1 represents the mixed acid sample without precipitation separation, and 2 represents the filtrate from which potassium fluorosilicate precipitate was separated by precipitation method.

[0080] The barium sulfate suspension method for quantitative sulfuric acid determination is simple, but because the original photovoltaic waste acid also contains fluorosilicate ions, barium ions easily react with fluorosilicate ions to form barium fluorosilicate precipitate, interfering with the sulfate determination results. After removing fluorosilicate through potassium fluorosilicate precipitation, the sulfate content was measured. In the table, the unprecipitated samples were affected by fluorosilicate ions, resulting in higher sulfate percentage measurements. After removing fluorosilicate ions, the sulfate percentage measurement decreased, indicating that separation improves the accuracy of the detection results. Analysis of the average relative deviation shows that the precipitation separation step has a small impact on the repeatability of the analysis, thus improving the accuracy of the results.

[0081] 2.4 Determination of F ions in photovoltaic waste acid to be treated:

[0082] When measuring F ions, a total ionic strength adjustment buffer solution is added to ensure that the ionic strength and ionic activity values ​​are consistent. The total ionic strength adjustment buffer solution is a mixed solution of glacial acetic acid, sodium chloride, and cyclohexanediaminetetraacetic acid, with a pH of 5.5–6.0.

[0083] The electrodes used for determining F ions are shown in the table below:

[0084] instrument effect PXSJ-216F Ion Meter Display ionic strength T-818-B-6 Temperature control electrode, real-time temperature monitoring 232-01 Reference Electrode Calculation of electrode potential reference pF-2-01 negative ion electrode Determination of fluoride ion strength in solution

[0085] Standard solutions of fluoride (sodium fluoride) with concentrations of 5 mg / L, 10 mg / L, 20 mg / L, 40 mg / L, and 60 mg / L were prepared. The potentials were measured using a fluoride-selective electrode. The logarithm of the fluoride standard solution concentration was taken as x, and the measured potential was y. A fluoride standard curve was plotted through linear fitting. The equation corresponding to the obtained fluoride standard curve is: y = -56.54log(C (F-) )+240.64, R 2 =0.9995.

[0086] Following the steps outlined above, using the aforementioned electrodes, take the filtrate after filtering out potassium fluorosilicate, adjust it with a total ionic strength adjusting buffer solution, measure the potential value y, and then substitute it into the standard curve to determine the concentration of fluoride ions in the treated photovoltaic waste acid. Substitute this into the following formula to further calculate the mass percentage content of fluoride ions in the waste acid.

[0087]

[0088] The standard curve was obtained (mg / L) is the percentage of fluoride ions extracted by substituting into the equation; m is the mass (g) of photovoltaic waste acid weighed in step 1; V is the volume of the test liquid prepared when testing fluoride ions (generally 0.05L).

[0089] Take the liquid from which fluorosilicate ions have been separated and determine the fluoride ion content. Measure the calibration curve using a fluoride ion-selective electrode. Figure 4 As shown in the table below, the final calculated mass percentage content of fluoride ions is as follows:

[0090]

[0091] 1,2 Note: All sample data were obtained by reacting with barium chloride to form a precipitate and then substituting the results into the standard equation. 1 represents the mixed acid sample that was not separated, and 2 represents the filtrate from which potassium fluorosilicate precipitate was separated by precipitation.

[0092] Fluoride ion selective electrodes are the simplest and fastest way to determine fluoride ions, but ions in the solution can easily cause interference. Therefore, dilution and the addition of ionic strength adjustment buffer solutions are generally chosen. However, waste acid solutions, especially those containing sulfate ions, release a lot of heat during dilution, which causes fluorosilicate ions to interfere with the fluoride ion measurement results. Therefore, removing fluorosilicate ions at low temperature can avoid the phenomenon of excessive fluoride ion concentration.

[0093] The above-mentioned mixed acid component detection of the present invention has a significant shielding effect on the mutual interference of fluorosilicate ions on fluoride ions and the mutual interference of fluorosilicate ions on sulfate ions. At the same time, it can detect each component one by one with high accuracy.

[0094] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for detecting fluorine-containing waste acid from photovoltaic projects, characterized in that, Includes the following steps: Step 1) Plot a standard curve for the nitrate standard. Use disulfonic acid phenol as an indicator to measure the absorbance value y of the photovoltaic waste acid to be tested at 420 nm. Based on the absorbance value y of the photovoltaic waste acid, obtain the nitrate concentration C corresponding to this absorbance value from the standard curve of the nitrate standard. (NO3-) The mass percentage content of nitrate in the photovoltaic waste acid to be tested is calculated using the following formula: Among them, W (NO3-) C represents the mass percentage content of nitrate in the photovoltaic waste acid to be treated. (NO3-) The concentration is determined based on the nitrate standard curve; m is the mass of the photovoltaic waste acid to be tested. Step 2): After adding saturated potassium nitrate solution to the photovoltaic waste acid to be tested, filter to obtain potassium fluorosilicate precipitate and the first solution. After separation of the precipitate, decompose it in water at 100℃. Titrate the decomposed solution with sodium hydroxide as titrant and bromothymol blue-neutral red as indicator. Calculate the mass percentage of fluorosilicic acid in the photovoltaic waste acid to be tested using the following formula: Among them, W (SiF62-) V represents the mass percentage of fluorosilicate in the photovoltaic waste acid to be treated; V is the volume of sodium hydroxide standard titration solution consumed in the titration; c is the accurate concentration of the sodium hydroxide standard titration solution; M (H2SiF6) is the numerical value of the molar mass of fluorosilicic acid, in grams per mole; m is the mass of photovoltaic waste acid detected in step 1). Step 3): Plot the standard curve of the sulfate standard. Add a barium ion-containing compound to the first solution to prepare a suspension. Measure the absorbance y of the suspension at 312 nm. Based on the absorbance y of the suspension, read the mass m of sulfate ions in the first solution from the standard curve of the sulfate standard. (SO42-) The mass percentage of sulfate in photovoltaic waste acid can be calculated using the following formula: Among them, W (SO42-) The percentage content of nitrate ions by mass in photovoltaic waste acid; m (SO42-) m is the mass of nitrate ions in the solution determined according to the standard curve; m is the mass of photovoltaic waste acid weighed in step 1. Step 4): Plot a fluoride ion standard curve with the logarithm of the fluoride ion standard solution's mass concentration as x and the measured potential value as y. After adding a total ionic strength adjustment buffer to the first solution and measuring the solution potential value y, determine the fluoride ion concentration in the solution from the fluoride ion standard curve. The mass percentage of fluoride ions in waste acid can be calculated using the following formula: Among them, W (F-) The percentage of fluoride ions in photovoltaic waste acid; C (F-) is the mass concentration determined based on the fluoride ion standard curve; m is the mass of photovoltaic waste acid weighed in step 1); V is the volume of the test liquid prepared when testing fluoride ions.

2. A method of detecting photovoltaic fluoroacid waste according to claim 1, wherein: The solvent used for the saturated potassium nitrate solution in step 2) is a mixture of water and ethanol at a volume ratio of 2:

1.

3. A method of detecting photovoltaic fluorine-containing spent acid as claimed in claim 1, wherein: In step 2), the precipitation reaction temperature is -20℃ and the precipitation treatment time is 20min, so as to effectively remove fluorosilicate ions from waste acid in the form of precipitation.

4. The method for detecting photovoltaic fluorine-containing waste acid as described in claim 1, characterized in that: The concentration of sodium hydroxide used in the titration in step 2) is 0.5005 mol / L.

5. The method for detecting photovoltaic fluorine-containing waste acid as described in claim 1, characterized in that: In step 4), the total ionic strength adjustment buffer solution is a mixed solution of glacial acetic acid, sodium chloride and cyclohexanediaminetetraacetic acid, with a pH of 5.5 to 6.

0.

6. The method for detecting photovoltaic fluorine-containing waste acid as described in claim 1, characterized in that: The linear range for fluoride ion determination by the fluoride ion selector is 0.0019 mg / L to 1900 mg / L. The concentrations of the fluoride ion standard solutions used to plot the fluoride ion standard curve are 5 mg / L, 10 mg / L, 20 mg / L, 40 mg / L, and 60 mg / L.

7. A method of detecting photovoltaic fluorine-containing spent acid as claimed in claim 1, wherein: The sulfate standard samples used to plot the sulfate standard curve were 0.2 mg, 0.4 mg, 0.6 mg, and 0.8 mg.

8. A method of detecting photovoltaic fluoroacid waste according to claim 1, wherein: The concentrations of nitrate standards used to plot the nitrate standard curve were 2 mg / L, 4 mg / L, 6 mg / L, 8 mg / L, and 10 mg / L.

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